In essence, a standard is an agreed way of doing something.
Standards are applied to many materials, products, methods and services. They are designed for voluntary use and do not impose any regulations. However, laws and regulations may refer to certain standards, making compliance with them compulsory.
Health and Safety standards aimed at workplace safety are a well known example, but you will find standards operating across many activities of daily life, for example IT standards to keep data safe, food safety standards to protect against contamination and many more.
The standards are laid out in a published specification that establishes a common language and an agreed, repeatable way of doing an activity or process.
Standards are designed for voluntary use, and do not impose any regulations.
However, laws and regulations may refer to certain standards and make compliance compulsory.
Observation of certain standards is often a requirement in order to comply legally with a contract.
Specification: highly prescriptive; the detailed absolute requirements for a product, material, process, service or system, and the procedures for checking conformity; the most commonly used standard.
Method: highly prescriptive; an agreed way of measuring, testing or specifying what is reliably repeatable in different circumstances and places
Guide: advice which reflects the current thinking and practice among subject experts.
Vocabulary: set of terms and definitions to help harmonize the use of language in a particular sector, field or discipline.
Code of Practice: recommendations for accepted good practice; incorporates a degree of flexibility in application.
Classification: designations and descriptions of different grades of a product.